The invention relates to an apparatus for manufacturing a glass stem, and more particularly to a universal stem mold having improved fillet-forming means. The glass stem comprises a number of lead-in conductors (or leads) usually ranging from five to twelve for a cathode-ray tube, CRT, each extending through a glass disk in a direction perpendicular to the plane of the disk and forming a circular array of leads. Typically, the leads comprise three component parts: an outer lead, an inner lead and a central press lead. The leads are round, copper sheathed, 42 percent nickel-iron wire, coated with fused sodium tetraborate. This lead material is commonly known as dumet. Alternatively, a one-piece lead of 52 alloy (52% nickel, balance iron) may be used. Where dumet is used, a glass fillet surrounds the junction of the outer, press, and inner leads to provide structural strength.
U.S. Pat. No. 3,201,216 issued to Handmann on Aug. 17, 1965 describes an apparatus for producing an electronic tube stem. Such a stem is usually made by inserting the leads in holes in a rotatable lower portion of a stem mold assembly which is mounted on an indexable turret. A glass cylinder is placed on the lower stem mold assembly around or within the leads (or both) and then the leads and the glass cylinder are heated to melt the glass. The glass cylinder is pressed into a disk in which the leads are embedded. Each of these operations takes place at an indexed position of the turret. During the heating operation, the leads, the glass cylinder, and the lower portion of the stem mold assembly, are rotated to uniformly heat the glass. During the pressing step, the upper portion of the stem mold assembly is pressed down onto the glass cylinder. Usually, the upper mold assembly is either rotated in synchronism with, and in properly indexed relation to, the lower mold assembly, or the lower mold assembly is stopped in properly indexed position relative to the stationary upper mold assembly. When the upper mold assembly is lowered to the pressing position, the leads extend into lead receiving holes in the upper mold assembly. As is known in the art, a tubulation is usually centrally disposed within the disk to permit evacuation and seal-off of the CRT. While most rotary stem machines have 24 or 30 lower stem mold assembly positions, there usually are only two, three or four upper mold assembly positions on a stem machine, the actual number reflect the preference of the machine designer. Where there are a plurality of pressing positions, reheating of the stem occurs between each pressing position (or station). The upper mold assemblies differ slightly from station-to-station and can be thought of, for convergence, as progressing from a rough press to a finished press. This change in upper stem mold assembly configurations makes it inconvenient and expensive to change the stem design, for example to change either the inner lead diameter or length, the fillet shape, or the location of a dummy fillet, i.e., a fillet without a lead therethrough, or the number of leads or dummy fillets per stem. Even if a stem machine is dedicated to producing only one type of stem, occasionally it is necessary to replace the portion of the upper mold assembly (called the mold block) which contacts the glass, because the hot glass of the stem eventually erodes the bridge between adjacent fillets resulting in a reentrant angle in the glass which causes cracked stems. Also the hot nickel-iron inner leads wear the lead accommodating holes in the mold block causing the originally circularly-shaped holes to become oblong resulting in displacement of the pin circle and/or bent leads.